This invention relates to an air intake system for a marine propulsion unit engine and more particularly to an improved induction system for such engines that insures against water ingestion to the engine and which permits the use of an air flow sensor without increasing the volume of the engine.
It is well known that many marine propulsion units are propelled by internal combustion engines. This is particularly true with respect to outboard motors wherein an internal combustion engine is positioned in the power head for driving a propulsion unit of the lower unit of the outboard motor. Conventionally, the intake passages for the engine are served by horizontally extending intake manifolds. This type of arrangement is employed regardless of whether the engine operates on the two stroke principle, as is more common, or on the four stroke principle.
Generally, because of the marine environment, the air is drawn directly from the atmosphere through the outer cowling and through an air silencing device positioned within the inner cowling. However, the horizontal disposition of the intake passages and the fact that the engine operates in a marine environment gives rise to the problem of ingestion of water into the engine combustion chambers during operation.
Although various water separation devices have been employed to avoid this problem, the water separators are normally provided in the outer cowling. That is, the induction system of the engine itself normally does not employ any water separation arrangement. It is, therefore, a principal object of this invention to provide an air intake system for a marine propulsion unit engine that includes an integral water separator.
It is a further object of this invention to provide an air intake system for a marine propulsion engine that is configured in such a way to insure that water will not enter the combustion chambers of the engine.
It is a further object of the invention to provide an improved and compact air intake system for an engine that includes a water separation arrangement.
In connection with engines and particularly those for marine application, it has been recently proposed to use fuel injection for the engine. The fuel injection system normally includes some form of air flow measuring device, either of the speed density type or of the mass flow type. With a speed density type, the engine can be quite compact in construction and a separate sensor can be provided for each cylinder. However, since the air flow is indirectly measured through suction pressure, the accuracy is low, particularly at low air flows and the air fuel ratio cannot be accurately controlled.
With a mass flow type, on the other hand, the air flow can be measured accurately, but the flow sensor generally is rather large and can add to the bulkiness of the engine construction. This is particularly true when the sensor is mounted on the induction system and externally of the engine, as is normally done. With such an arrangement, this can not only provide problems with space for an individual engine, but it can restrict the maneuverability of the associated watercraft if plural outboard motors are employed on a single boat. That is, if the cowling is sized so as to clear the air flow sensor, then the turning or steering movement of the outboard motors may be restricted.
It is, therefore, a still further object of this invention to provide an improved and compact arrangement for sensing the air flow to an engine without increasing significantly upon its bulk.